The control system is a small part of the investment in a water or wastewater treatment plant, but it decides how the plant runs for as long as it is in service: how stable the water quality is, how much energy and chemicals are used and how many people are needed on site. This guide explains what an automation package consists of, what its cost depends on and which documents make a reliable offer possible.
What an automation package includes
- Field instruments — sensors for flow, level, pressure and water quality such as pH, conductivity, turbidity, dissolved oxygen and chlorine. See analysers and sensors.
- Motor control — one feeder per pump, blower, mixer and valve actuator, with a direct starter, soft starter or frequency converter.
- PLC — the controller with its input and output modules reads the signals, runs the sequences and control loops and switches the drives.
- Operator level — a touch panel on the control cabinet for small plants; a SCADA system with plant overview, trends, alarms and reports for larger ones.
- Communication — the network between controller, remote I/O stations, drives and SCADA, and a secured remote connection for support.
- Engineering — circuit diagrams, the functional description, the software, tests and documentation.
The cabinets themselves are described on our electrical and automation panels page.
The three levels of automation
| Level | Typical for | What the operator gets |
|---|---|---|
| Local control | Single machines and small package units | Start and stop at the machine, simple interlocks, fault lamp |
| PLC with operator panel | Skid-mounted plants and small treatment plants | Automatic sequences, setpoints and alarms on a touch panel, remote alarm by message |
| PLC with SCADA | Plants with several process stages or several sites | Central overview, trends, reports, user management, remote operation |
Most plants we supply are on the second or third level. A higher level costs more to build and less to run, because faults are seen earlier and fewer rounds on site are needed.
What drives the cost
- Number of signals — every sensor, valve and motor needs inputs and outputs, wiring, a place in the software and a test. The signal count is the best single measure of the size of an automation project.
- Number and size of drives — motor feeders make up most of the cabinet volume. Frequency converters cost several times as much as direct starters, and large drives need larger switchgear and cables.
- Instruments — a level switch costs little, an online analyser for chlorine or organic carbon a great deal. The instrument list often decides whether an offer is high or low.
- Software scope — the number of sequences and control loops, the SCADA pictures, reports and interfaces to other systems.
- Availability — redundant controllers, power supplies and networks, and an uninterruptible power supply.
- Site conditions — outdoor cabinets, air conditioning, corrosive atmosphere and explosion-protected areas.
- Standards and documentation — operator standards for makes and software structure, witnessed tests and the depth of the documentation.
How the cost is typically divided
| Part of the project | Typical share |
|---|---|
| Control cabinets with PLC, switchgear and drives | 35–50 % |
| Field instruments | 15–25 % |
| Engineering and software | 20–30 % |
| Testing, commissioning and documentation | 10–15 % |
Typical shares for water and wastewater plants. Cabling and installation on site are usually quoted separately, because they depend on the distances and on who carries out the work.
Where automation pays back
- Energy — blowers and pumps controlled by frequency converters follow the demand instead of running at full speed. Aeration is the largest electricity consumer of a treatment plant, so oxygen control is usually the first measure.
- Chemicals — dosing in proportion to flow or to a measured value avoids both overdosing and limit violations. Details under chemical dosage systems.
- Staff — alarms by message and remote access replace routine rounds, above all at night and at weekends.
- Reliability — trends show a fouling membrane, a worn pump or a drifting sensor before the plant fails.
- Evidence — automatic reports document flows and discharge values for the authority.
Modernising an existing plant
Many enquiries concern plants whose controllers are no longer supported. The usual procedure keeps the plant running:
- Survey of the existing cabinets, signals and software.
- New control cabinet or new controller in the existing cabinet, built and tested in advance.
- Change-over in stages, one plant section after the other, each with a short planned stop.
- Function test of every signal, then the next section.
Field devices and cabling that are in good condition are kept. This limits both the cost and the downtime.
Documents that make a reliable offer possible
- Process flow diagram or P&ID.
- Motor list with power and type of starting.
- Instrument and signal list, or at least the number of analogue and digital signals.
- A short description of how the plant is to be operated.
- Preferred makes of controller and drives, if there is a standard on site.
- For modernisation: photos of the cabinets and, if available, the existing circuit diagrams.
With these documents we can name a budget price; a binding offer follows after the scope has been clarified. More about our approach on the automation page.
Frequently asked questions
What does it cost to automate a water treatment plant?
It depends on the size of the plant, measured by the number of signals and drives, and on the instruments and software required. A package plant with one cabinet and a touch panel costs a fraction of a treatment plant with a SCADA system. The lists named above are enough for a budget price.
Is a SCADA system necessary for a small plant?
Not always. A touch panel with trends, alarm messages and remote access covers the needs of many small plants. SCADA becomes worthwhile when several process stages or several sites are to be supervised from one place, or when reports are required.
Which PLC should be chosen?
The one your maintenance staff know and for which spare parts are available locally. In Europe this is most often Siemens S7-1200 or S7-1500; in other regions Allen-Bradley is common. The software should be delivered open and documented, so that it can be maintained without the original supplier.
How long does an automation project take?
For a plant of medium size, a few months from the order to commissioning: engineering and software, cabinet building, the factory acceptance test, then installation and commissioning. The delivery time of the cabinets and of some instruments is often what decides the schedule.
Can the plant be operated remotely?
Yes. A secured connection allows monitoring, alarm handling and, where the operator allows it, operation from a distance. Functions that affect safety remain interlocked in the controller on site.
Send us your process diagram and motor and signal lists via our contact page. We will prepare a budget offer for cabinets, instruments, software and commissioning.